CT is used to provide doctors with a cross-sectional picture of a patient's internal organs and tissues; and if a puncturing operation is to be performed, the CT-scanner provides the doctor with image data from which the doctor determines the puncturing position, the direction and the depth for a puncturing device so as to reach the target site. In some cases, the puncturing device is manipulated without employing any device for guiding the puncturing needle, but often some kind of guiding device is used.
A variety of guides employed to properly position a medical instrument within the body of a patient are known in the state of the art. U.S. Pat. No. 4,733,661 discloses a handheld guidance device for use in conjunction with a CT scanner. This guidance device comprises a base including a bubble level and a needle support arm pivotally secured to the base, and a cooperating protractor indicates the relative angular relationship between the needle support arm and the base. Needle guides are provided on the support arm for slidingly supporting a catheter at a desired angle as the catheter is inserted into the body of the patient. With this device, the direction to the target site has to be set with two separate operations, one that adjusts the elevation angle of the support arm and one that rotates the guidance device.
In U.S. Pat. No. 5,263,956 is shown a ball joint for holding a neurosurgery tool in a predetermined orientation relative to a patient's skull. The ball joint, which is provided with a bore, is rotatably positioned in a socket formed in a plate, and a neurosurgery tool can be positioned in the bore to extend through the bore into the patient's brain. Set screws are provided to hold the neurosurgery tool stationary relative the bore of the ball and to hold the ball stationary relative the plate. A retainer ring holds the ball against the plate. The bottom of the plate is provided with spikes for gripping the skull.
In DE-19,808,220 A1 is shown another guiding device. This guiding device comprises an attachment plate and a ball joint for guiding a needle. The bottom side of the attachment plate is provided with an adhesive, so that the guiding device can be securely positioned on a patient's skin. The ball joint is provided with a clamping means, which allows the needle to be positioned in a continuously variable spatial direction.
U.S. Pat. No. 3,021,842 discloses a similar guiding device that also comprises a ball joint, which in this case is provided with a pinion. With the pinion, the ball can be turned in a socket through a wide range of angles.
A common feature of the devices known in the state of the art is that the point of entrance for a puncturing device, e.g. puncturing needle or a biopsy needle, through a patient's skin varies with the entrance angle, or, with other words, the rotation centre of the directional adjusting means is not located at the entrance point. This means that it is not possible to position the distal tip of a puncturing device at the puncturing point in a first operation and then, in a second operation, set the entrance angle of the puncturing device without changing the entrance point of the puncturing device. In some applications this is a considerable disadvantage, as will be described below.
The object of the present invention is to refute the above-identified drawback with known devices in the art of puncturing guidance.